Abstract

Have you ever wondered how nutritionists know how many Calories a certain food contains? In this project you'll learn a method for measuring how much chemical energy is available in different types of food. You will build your own calorimeter to capture the energy released by burning a small food item, like a nut or a piece of popcorn. This project gives a new meaning to the phrase "burning calories."

Objective

The goal of this experiment is to determine the amount of chemical energy stored in food by burning it and capturing the heat given off in a homemade calorimeter.

Credits

Andrew Olson, Ph.D., Science Buddies

USC Biology Department, 2004. Burning Calories: The Energy in Food.
Biology Department, University of Southern California. Out of print.

APA Style

Science Buddies Staff.
(2014, October 6).
Burning Calories: How Much Energy is Stored in Different Types of Food?.
Retrieved March 3, 2015
from http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p012.shtml

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Introduction

You know that the energy that keeps your brain and body going comes from the food you eat. Your digestive system and the cells in your body break down the food and gradually oxidize the resulting molecules to release energy that your cells can use and store.

In this project you will learn a method for measuring how much chemical energy is stored in different types of food. You will oxidize the food much more rapidly, by burning it in air. You'll use a homemade calorimeter to capture and measure the heat energy released by burning. The basic idea of a calorimeter is to capture the released heat energy with a reservoir of water, which has a high capacity for absorbing heat. The temperature of the water reservoir is measured at the beginning and at the end of the experiment. The increase in the temperature (in °C) times the mass of the water (in g) will give you the amount of energy captured by the calorimeter, in calories. We can write this in the form of an equation:

Qwater = mcΔT

where:

Qwater is the heat captured, in calories (cal);

m is the mass of the water, in grams (g);

c is the specific heat capacity of water, which is 1 cal/g°C (1 calorie per gram per degree Celsius); and

ΔT is the change in temperature (the final temperature of the water minus the initial temperature of the water), in degrees Celsius (°C).

Let's work through an example to make sure that the equation is clear. (We'll use made-up numbers for the example. You'll have to try the experiment for yourself to get actual measurements.) So let's say that we start out with 100 g of water in the calorimeter (m = 100 g). The initial temperature of the water is 20°C. After burning up some small piece of food, we measure the water temperature again, and find that the final temperature is 24°C. Now we have all of the information we need to calculate the amount of heat captured by the calorimeter:

Now you can see why the specific heat capacity of water has such strange units (cal/g°C). Notice that the grams (g) from the mass of the water and the degrees Celsius (°C) from the change in temperature cancel out with the grams (g) and degrees Celsius (°C) in the denominator of the units for specific heat. That way you are left with units of calories (cal), which is what you want.

A Note on Units

A calorie (lowercase "c") is actually defined by the heat capacity of water. One calorie is the amount of energy that will raise the temperature of a gram of water by 1°C. When we talk about food energy, we also use the word "Calorie," (note uppercase "C") but it is a different unit. It is the amount of energy needed to raise the temperature of a kilogram (= 1000 grams) of water by 1°C. So a Calorie is the same as 1000 calories. Or, to put it another way, 1 Calorie = 1 kcal. So in this project, for food Calories we will be careful always to use an uppercase "C".

Eating a balanced diet is fundamental to good health. This project will give you a chance to learn about how much energy your cells can extract from different types of food. It is important to remember though, that energy is only one measure of nutritional value. As you are doing your background research on this project, try to find out about other measures of a balanced diet in addition to food energy.

Terms and Concepts

To do this project, you should do research that enables you to
understand the following terms and concepts:

calorie (cal),

kilocalorie (kcal),

Calorie,

calorimeter,

oxidation,

Recommended Dietary Allowance.

Questions

The reference level for a normal diet is 2000 Calories. How many calories is this?

What are the basic chemical structures of fats, sugars and proteins?

Do these types of molecules differ in the amount of energy they contain?

Which of your food items do you think will release the most energy? Why?

What is meant by a "balanced" diet? Why is it important?

Bibliography

The U.S. Department of Agriculture is a good online source of information about nutrition. The links below are for general information, key nutritional recommendations and special pages with information for kids:

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Materials and Equipment

A project kit containing most of the items needed for this science project is available for puchase from AquaPhoenix Education. Alternatively, you can gather the materials yourself using this shopping list:

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Experimental Procedure

Safety note: Adult supervision is required! As with any project involving open flame, there is a fire hazard with this project. Make sure you work on a non-flammable surface. Keep long hair tied back. Be careful handling the items used in this experiment as they may be hot! Wear safety glasses.

Figure 1. Diagram of Homemade Calorimeter

Constructing the calorimeter (refer to the diagram above).

Select two cans to build your calorimeter. They should nest inside one another. The smaller can needs to sit high enough so that you can place the cork, needle and food item beneath it.

Remove the top and bottom from a coffee (or similar-sized) can, so that you have a cylinder open on both ends.

Use a hammer and nail to make holes in the bottom (to allow air to in to sustain the flame).

Punch holes at opposite sides of the smaller can for the support to pass through. The diagram labels the support as a glass rod, but you can use a wood dowel, a pencil, or a metal rod for the support. Your support needs to be longer than the width of your large can.

Grasp the needle (or wire) and push its blunt end into the cork. You will impale the food to be tested on the sharp end of the needle. (If you use wire, you can wrap it around the food item to be tested. Don't use insulated wire!)

The smaller can will hold the water to be heated by burning the food samples. Use the graduated cylinder to measure how much water you use; the can should be about half-full. Put the supporting rod in place through the two holes.

Figure 2. A top down view of the homemade calorimeter is shown here.

Weigh each of the food items to be tested and record the weight.

Fill the small can about half-way with a measured amount of distilled water.

Measure the initial temperature (Ti) of the water.

Impale the food item on the needle (or wrap the wire around it).

Have your calorimeter pieces close at hand, and ready for use.
For more information on how to properly weigh items see Chemistry Lab Techniques.

Place the cork on a non-flammable surface. Light the food item (the nuts may take awhile to catch fire).

When the food catches fire, immediately place the large can around the cork, then carefully place the smaller can in place above the flame.

Allow the food item to burn itself out.

Carefully remove the small can by holding the ends of the supporting rod, and place it on a flat, heat-proof surface. The can will be hot, so be careful.

Carefully stir the water and measure the final temperature (Tf). Make sure the thermometer has reached a steady level before recording the value.

When the burnt food item has cooled, carefully remove it from the needle (or wire) and weigh the remains.

Repeat steps 2–13 for all of the food items. It's a good idea to repeat the measurement with multiple samples of each food item, to insure consistent results.

Analyze your data. Calculate the energy released per individual food item (in calories and Calories), and the energy per unit weight of each food item (in calories/gram and Calories/gram). From your individual results, calculate average values for each food type.

Questions

Which food type released the most energy per gram?

Can you calculate the average energy (in Calories) for each type of food item you tested?

Do you think the amount of Calories you measured is likely to be higher or lower than the true value for each food item? Why?

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Variations

Do background research to find out the approximate proportions of the different basic food chemicals (fats, carbohydrates, proteins) in each of the food items you tested. Can you draw any conclusions about the relative amounts of energy available in these different types of chemicals?

Do background research to find out the chemical composition of candle wax (paraffin). Design an experiment to determine the amount of energy released per gram of candlewax.

Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Related Links

If you like this project, you might enjoy exploring these related careers:

Dietitian or Nutritionist

Ever wondered who plans the school lunch, food for patients at a hospital, or the meals for athletes at the Olympics? The answer is dietitians and nutritionists! A dietitian or nutritionist's job is to supervise the planning and preparation of meals to ensure that people—like students, patients, and athletes—are getting the right foods to make them as healthy and as strong as possible. Some dietitians and nutritionists also work to educate people about good food choices so they can cook and eat their own healthy meals.
Read more

Food Science Technician

Good taste, texture, quality, and safety are all very important in the food industry. Food science technicians test and catalog the physical and chemical properties of food to help ensure these aspects.
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Chemist

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Chemical Technician

The role that the chemical technician plays is the backbone of every chemical, semiconductor, and pharmaceutical manufacturing operation. Chemical technicians conduct experiments, record data, and help to implement new processes and procedures in the laboratory. If you enjoy hands-on work, then you might be interested in the career of a chemical technician.
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